Well, there's only one problem with casting to void *: while converting the function pointer to another *is* standard-compliant, and GCC is being just hypersensitive here, casting a function pointer to void * isn't, though it is a common extension (http://port70.net/~nsz/c/c11/n1570.html#J.5.7).

Pedantically the correct way is to cast to a function pointer with no prototype (empty parentheses) and from that to the target type. See for example. See for example https://godbolt.org/g/FdPdUj